Thermoelectric modules are used both as heating/cooling elements, for example as so-called Peltier elements, and as thermoelectric generators. The fundamental structure for both applications is the same in this case. Initially, externally an electrically non-conductive layer, e.g. made from ceramic ensures electrical insulation. Thermoelectric active elements, which are connected to electrical conductor tracks, are located in the interior of the thermoelectric module. Solder is often used as joining material between the conductor tracks and the thermoelectrically active element. The thermoelectric modules are usually connected to a ceramic side on the cold side and to the metallic side on the hot side. In order to allow a simple welding of the thermoelectric module, it is advantageous to apply the ceramic onto a metallic base material. Often, on the hot side of the thermoelectric module, the high temperature is generated by an exhaust combustion gas, which still contains oxygen and in particular also elevated levels of water, so these exhaust combustion gases act in a strongly oxidising manner. The thermoelectrically active element is changed by the oxidation, wherein gaseous, that is to say volatile, oxides can also be formed. In addition, the exhaust gas entrains hydrocarbons and carbon black, which are deposited after condensation at temperatures below the dew-point temperature as a parasitic electrically-conductive and heat-conducting layer on the thermoelectrically active element. Thus, the exhaust gas is therefore to be kept away from the thermoelectric active element for a wide range of reasons.
In addition to the risk of oxidation, certain thermoelectrically active elements, which for example contain tellurium (Te) or antimony (Sb), have a tendency towards element vaporisation. This is important in the case of Sb-base materials, such as for example CoSb3 and Zn4Sb3, as these thermoelectrically active elements are intended in particular for use at elevated temperatures up to 400° C. and even beyond that.
Amorphous electrical modules for preventing the oxidation are already known, which are completely enclosed in a housing, for example made from high-grade steel, and in the case of which the interior is filled by means of an inert gas. As a result, although the oxidation can be inhibited, the previously described element vaporisation cannot. In addition, a gap is present between the metallic housing and the interior, which in turn reduces the efficiency of the thermoelectric module.
A thermoelectric module is known from U.S. Pat. No. 7,461,512 B2, the interior of which is filled between the thermoelectrically active element and a housing by means of a sol-gel. By means of thermal conversion, one obtains a coating of the thermoelectrically active element with a so-called aerogel. As the pore diameter of this aerogel is much smaller than the average free path length of the vaporised element, the element vaporisation can be reduced by a factor of 10. An aerogel of this type does not protect against an oxidation however.
A generic thermoelectric module with a fluid-tight housing, in which at least one thermoelectrically active element is arranged, is known from DE 10 2011 005 246 A1. In this case, the housing is assembled from two housing elements, namely from a metallic housing element and a further housing element, which is arranged on the side of the metallic housing element which has a ceramic layer. It is therefore suggested that an electrical insulating layer is applied on a metallic housing material and the actual conductor tracks are only applied thereupon.
A thermoelectric module is known from DE 10 2012 208 295 A1, which has a housing element and a thermoelectric element arranged on the housing element, wherein a joint seam region is provided between the thermoelectric element and the housing element, which was formed by compressing a joining material. Further, the thermoelectric module comprises a further housing element, which is connected to the housing element to form an optionally fluid-tight housing, wherein the thermoelectric element and the joint seam region are arranged in the housing.